HobbyKing Cosmic Wind

HK Cosmic Wind
Build and Flight Review
© Marc A. Volovic, 2014, marc@bard.org.il

I got the Cosmic Wind just after crashing another fast-ish plane. In a way - I got it as a kind of a rebound - the plane I crashed was a kit build and I murdered it on the very second flight, in a moment of inattention. So - I decided to get something simple, easy to build and fast-ish too.

It arrived from Hong Kong in a fairly small box, with no component damage. The part count is not large, which is good. Attractive dark blue colour, black and white chequerboard on wing bottom.

So - let’s do a parts review and see if anything is missing, said I. Opened the manual and… Ummm, parts missing - NO MANUAL. Not in box. Not online. Not anywhere, in fact. Now, I am reasonably experienced ARF assembler and can wing it, but for anyone inexperienced, not having a manual would be is a major problem. And even for me - no manual means guessing the centre of gravity and the (much more critical in a fast-ish plane, throws). Minus one point to HK.

I found the manual to the original Cosmic Wind, made by Great Planes online. The planes are quite similar and the GP manual can be used to the HK version, except where noted in this write-up.

Looking the plane over, the machine seems reasonably well made. Wings are covered well, with only minimal need to re-iron the covering here and there. The fibreglass is fine, too. Wood fixtures are more or less ok, except for one spot (the left wing-attach blind nut wood support is striated and needs re-gluing). The horns, clevises and pushrods look a bit flimsy, but for a plane this size they are sufficient.

A major improvement, in comparison to the Great Planes parent, are the linkages. Gone are the horrible GP double collar BDSM arrangements, their place taken by simple screw-on plastic clevises and Z-bends. Plus one point to HK. Maybe even plus two.

The machine will require three servos - one for ailerons, one for rudder and one for elevator. For a moment, I struggle with the desire to mod the model and add a second aileron servo, allowing me to program spoilerons, but idleness wins - no mod, we’ll go with a single servo. I chose to use Savox SH-0257MG micro servos - fast, quite strong, very precise and, for their quality, quite cheap.

Motor choice is quite large - from the Rimfire 10 (from the GP manual) to wild inventions, like EDF motors and hyper fast rotating small things. I tried three - one which is close to the Rimfire and two nutty ones.

Quite early on, I decided to select equipment with lighter all-up weight in mind. Thus, I lovingly caressed and then discarded the wheel pants. They are sexy, but they add a lot of weight.

Wing Assembly
Wing construction is a snap - joining and gluing the halves, using the carbon tube (which fits well) and the rotation stop is easy and simple. Ailerons go into their slots quite precisely and the single servo and the control linkage is easy and trivial. I considered sealing the gap between the aileron and the wing, but for now, decided not to.

However, while working on the wing, I started thinking of the colour scheme. The ‘lil poppet is all of 92cm wingspan and will go reasonably fast. Say, 130-150kph. At that size and that speed, the blue and the white-black will merge and look black. Oh my, looks sexy sitting but orientation will be hard. Rummaging through the parts bin, I got a large panel of orange covering film and ironed it on the top right wing. There. I am tempted to dock HK for the colour scheme - but no.

Last, I tried to stuff the two bitty thingies they supply for the wing mounting. Too long and not a good fit. Fixing that took a fair amount of fiddling, but got done in the end.

Fuselage Assembly
Not much to construct, here. Stuff the servos in for a placement check, stuff the motor in for same, strengthen the bad blind nut, check control linkages freedom of movement, check that the battery hatch retention is… is WHAT? Two bitty magnets that would have trouble holding a butterfly wing to a fridge door? Ye gods of magnetism, give me strength. Minus two points to HK.

So here we go - dremel a small long slot in the hatch, dremel an indentation in the fuse rim, glue in a piece of wood with a nice hole in it and - we have a hatch latch. Yay!

The last thing to do is screw in that thingy for the tailgear. Thingy, thingy, come to me. Thingy! I am waiting. No thingy. In fact, thingy is missing. Drat, but no big deal - manufacture one of my own, from carbon. All fine.

A let’s bolt on that tailgear now… What is that tailgear made off? No, really? Bendy, mamby-pamby thin wire. It is weak, the wheel stop is fiddly and I suspect it will make ground handling annoying.

Finishing touches, including the canopy are very simple. Decided not to add a pilot head.

Gizzards and Balancing
Gizzards are simple - two servos, final placing like the GP manual. Linkages and so on and so forth. The one problem - motor. The one I used initially (NTM 3536-1800) proves heavy (121g). The NTM 2836-2700 weight 70g and fits well but has a short shaft and my collets are too deep for it. So, order an SK3 3530-1460. I like the SK3 more than NTM, anyway - the wiring looks better and is far bendier. It will also allow me to use a lighter ESC.

The SK3 requires slight widening of the motor mounting slots in the firewall, but that is quite simple - three minutes with a careful dremel. CG (52mm behind LE) directly from the GP manual. Throws (5mm up down ailerons, 6mm elevator, 6mm rudder) ditto. Rx - the smallest and lightest I have in my bin - FrSky TFR4B. The ESC - as small as can feed the motor, a YEP 40A. I love the YEP speed controls - light, work well, use SBEC’s even on the smaller ones.

Down the road, I will switch to nuttier motors.

Battery - 2200 3S (200g) and move to balance. Props, an APC 8x6 for the test and 8x8 for the normal flight regime.

All up weight with battery - 1060g. We are ready.

Preflight
A single maiden is never good. Let’s do things in threes. Use the new Futaba 12FGA. Maiden the giftie-extra-profile (a discard plane I was given by a friend. Flies like a turd. Yech). Ok, bind the Rx to the radio. What do I mean by bind? Ah - simple. This is a Futaba 12FGA. I got it yesterday. Replaced my 14SG. No, I have not yet had time to learn how to feed in D/R or expo. Did I tell you j’ai des grandes couilles? Well, I do!

Line ‘er up. Darth Vader cue!

Flight
Take off: A test pre-takeoff taxi - plane veers badly to the left and needs a more firm hand on the rudder. The damn chicken-wire tail-wheel does not help at all. I might want to replace it. Sit the plane on the ground properly, take a breath. Fear is the mind-killer. I will face my fear. I will permit it to pass through me and when it has passed, only I will remain. Feed power, a bit too quickly and, after some 3 feet, the plane jerks off into the air at a 50 degree angle and off we go, bank left, three clicks down to correct upswing, two right. It gets small real fast. Blurry, too. Oh damn, I have the wrong spectacles on - the reading ones. This is a… fear is the mind killer.

Flight: Ok - wrongo specs, late in the day - serene flight. Throttle down to some 20% and fly long. See how she turns, bank start feeding rudder... mush and wing-drop! Feed power back in, bank out and add power. Breathe. Ok, let’s fly it like I stole it - hard bank and hard pull at 40% throttle, she turns well, no mushiness. This is how, then. Three passes. Drat, the wrong specs make things hard. She gets blurry real fast. Lucky that orange panel on wing. LANDING! Bank slightly away from base, turn in and let her drop straight into…

Landing: Long almost unpowered drop, reasonable angle but steeper than I like. Feed in a bit of power to reduce the sink rate, ah, good. Almost flat, a bit fast. Now for a tiny flare… WHOA! Up she goes, gaining a chunk of altitude. Drop the motor, drop the elevator and boing, boing, boing - kangarooing we go. Stiff gear help with that. Ah, and then roll and stop. Curse that landing. We are back, in one piece, no D/R, no expo, wrong spectacles… Whoo. J’ai des grandes couilles.

Summary
When I started building it, I kept score. Then, I stopped. This plane is greater than the sum of its parts. So - this being so, let’s have a bottom line.

This is one cool plane. Not for beginners. Really, really not for beginners. Requires flying and attention. I did not yet push it and need at least three-four more acclimatization flights before I feel comfortable with it.

But it is a very fun plane, very good-looking and sexy plane, exhilarating plane. That is what we all want, after all. Indeed, it is surprisingly easy to fly if you have a good memory and are not easily startled. Landings should be made long and flat, for the stiff gear make kangarooing too easy.

It is simple and fun to build, has enormous internal space for such a tiny device, can take a large battery and be used with a very wide selection of power trains. Easy to modify those bits that need modifying (battery hatch) or benefit by modifying (spoilerons).

It is a lovely looker and I heartily recommend it for the late intermediate flyer.

Equipment Used
Plane - Cosmic Wind
Motor 1 - NTM 2836-2700 (planned for, unused because of spinner limitations)
Motor 2 - SK3 3530-1460 (used in test-flight)
Motor 3 - NTM 3536-1800 (used in planning and initial CG checks)
Servos - Savox SH-0257MG
ESC - YEP 40A
Prop - APC 8x6E (used in test flight), APC 8x8
Battery - 3S 2200mAh 30C
Transmitter - Futaba 12FGA
Receiver - FrSky TFR4-B
Miscellaneous - battery hatch latch, cable management loops, spare bits of glow fuel line, 45mm spinner, 4mm aluminum collet, 10cm servo extensions, glues, velcro, locktight, etc

Movie - https://www.dropbox.com/s/xkjhwwb18x...2017.17.18.mov
(shot by Pablo Kohan)


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